A major objective of this renewal is the continued development of various chemical carcinogenic regimens which would make possible a more discrete and specific analysis of macromolecular interactions and cellular events in the evolution to malignancy. We will examine in detail the single-exposure technique (70% hepatectomy plus administration of carcinogen) by utilizing the highly synchronous regenerative response of the weanling rat at various phases with carcinogens of diverse chemical class. Further, we will attempt to better quantitate the increased sensitivity of the dividing hepatocyte by comparing the dose of carcinogen required to induce it to malignancy with proportionately greater doses in normal rats. The process of carcinogenic evolution in these experiments and those described subsequently will be monitored by determination of morphologic evolution, circulating levels of alpha fetoprotein and cytogenetic composition. These modalities will also be applied to the tumors which result. We will continue to examine a synergistic two-carcinogen regimen which may make possible the induction and segregation of crucial stages in the carcinogenic sequence. To further these studies a number of carcinogen combinations will be examined. It appears that these experiments, using carcinogens which interact with macromolecules by differing mechanisms may yield insight into the aggregate perturbation(s) of these molecules which result in malignant evolution. Lastly, we will continue to study a system developed in our laboratory for the testing and study of carcinogens in vitro. The fertilized oocytes of xenopus laevis are exposed to carcinogens, their metabolic derivatives and non-carcinogenic analogues at various stages of development and are then examined for teratogenic and lethal sequelae.